Direction finding system



J. H. NEWITT DIRECTION FINDING SYSTEM Nov. 2, 1948.

Filed llay 4, 1946 .vukkin U 55 QQQMUMQ INVENTOR. JOHN H. NEW/T7 ATTOIPNEY Patented Nov.;2, 1948 oFFl cE DIRECTION FINDING SYSTEM John H.Newitt, Maplewood. N. 1., assignor to Federal Telephone and RadioCorporation, New

York, N. Y., a corporation of Delaware Application May 4, 1846, SerialNo. 667,273

This invention relates generally to direction finding systems andparticularly to electronic goniometers therefor.

An object of the present invention is the provision of an improvedelectronic gon om ter.

Anohe'r object of the present invention is the provision of an improveddevice for combining the output derived according to two radian actionpatterns from an antenna system.

Ano her object of the present invention is the provision of anelectronic goniometer which is characterized by a very high degree ofbalance.

Another object of the present invenion is the provision of an electron'cgoniometer in which matching of tubes is not necessary in order toobtain radio frequency ba ance as the electronic goniometer according tothe present invention is very uncritical in operation as regards baance.

Another object of the present invention is the provision of an improveddirection finding system employingwan electronic goniometer embodying mypresent invention.

In accordance with a feature of the present in.

vention, the electronic goniometers are comprised of two balancedmodulators. For satisfactory operation of the electronic goniometer andfor proper balance of each of the balanced modulators, it has heretoforebeen considered necessary to very carefully match the tubes contained inthe balanced modulators. Even. with this precaution, such modulatorshave been critical in re- 1 Claim. (Cl. 343121) not critical inoperation in respect to radio ire 'quency balance.

Other and further objects of the present invention will become apparentand the invention itself Will be best understood from the followingdescription of an embodiment thereof, reference being had to. thedrawing, in which the figure is a schematic and block diagram of adirection finder including'an electronic goniometer in accordance withthe present invention.

Referring now to the figure, directive reception The radiation patternproduced by loop antennas l and 2 may be effectively rotated by means ofan electronic goniometer generally designated by the numeral 3, whichconsists of two balanced modulators 4 and 5 associated with loops i andZrespectively. Balanced modulators 4 and 5 each include two tubes 6 andI, and 8 and 9, resp ct vely which tubes may be triodes of theindirectly heated type, and which preferably may be di k-sealed tubes oflow inter-electrode capacitv and low impedance leads, such as forexample, the well-known lighthouse tube.

- In accordance with the present invention, the loo an ennas I and 2'are connected by transmission lines in and H to matching terminating reistors l2 a d it. ea h having a value equivalent to the characteristicimpedance of lines it and ii. Re istors I2 and 53 also serve as thecathode resistors for the tubes in balanced modu= lators i and 5respectively. For this purpose, resistor i2 is divided into two halves82a and iZh with one end of I211 coupled to the cathode of tube 8 andwith one end of iflb coupled to the cathode of tube 7. The mid-pointbetween these halves is connected to a point of reference potential orground. Likewise resistor i3 is divided into two halves I30. and i322with the free ends of each half being connected to the cathodes of tubes8 and 9 respectively and the connecting point between the two halvesbeing grounded. The signal energy derived from loops i and 2 isimpressed upon tubes 6 and l, and i3 and 9 by appiication of saidsignals across the cathode resistor to the cathodes of said tubes. aremaintained at an R. F. level above ground. On the other hand, the gridsof tubes 6, l, 8 and 9 are mainta ned at ground radio frequencypotential by means of condensers I i-4? which couple said grids toground at the operating radio frequency. This frequency, whichis thecarrier frequency of the incoming signal picked up by loop antennas land2 may be for example as high as 150 megacycles or higher.

The heaters-or filaments of tubes ti and i are connected in parallel,with one side being connected to ground directly and the other sidebeing connected through a condenser iii to ground through a radiofrequency choke coil l9. Similarly the filaments of tubes 8 and 9 areconnected in parallel with one side being connected to ground and theother side being connected in series with a choke coil 20 and acondenser 21 to ground. The choke coils l9 and 20 serve to isolate theradio frequency currents in the The cathodes 1 aecaero parallelconnected filaments of balanced modulators d from that in balancedmodulator 5.

To provide for effective shifting of the radiant 2. The output ofoscillator 22 is fed to a phase shifter 23 which shifts one of itsoutputs 90 with respect to the other so that the output leads 24 and 25,which are balanced with respect to ground, are 90 out of phase withoutput leads 26 and 21 which are likewise balanced with respect toground. Leads 24 and which are 180 out of phase With each other areconnected to the primary of a transformen- 28 whose tapped sec ondaryhas its tap connected to ground as at 29 and the ends of which secondaryare connected in series with radio frequenc choke coils 30 and 3| to thegrids of tubes 6 and I respectively. The ends of the secondary oftransformer 28 are also connected through grid resistors 32 and 33 toground.

The low frequency or modulating energy from oscillator 22, which hasbeen phase shifted in phase shifter 23, is applied through leads 26 and21 to the primary of a transformer 34 whose tapped secondary has the tapconnected to groundand the two loose ends of said secondary connected inseries with radio frequency choke coils 36 and 37 respectively to thegrids of tubes 8 and 9. These ends are also connected through gridresistors 38 and 39 to ground. Thus the modulating voltages are appliedto modulators d and 5. While condensers l4-ll ground the grids of tubes6-9 at radio frequency, these condensers have a substantial reactance atthe low frequency of the modulating voltages derived from oscillator 22and consequently these grids are substantially above ground potential atsaid low frequency.

-To balance balanced modulators 4 and 5, two sources of balancingvoltages 40 and 4| have their positive sides connected to ground .andtheir negative sides connected respectively to the arms ofpotentiometers 42 and 43 whose resistors are respectively connectedacross the secondaries of transformers 28 and 34. By adjusting thepotentiometer arms, the Gm curves of tub-es 6 and 1 and of tubes 8 and 9are adjusted to equality.

Since the grids of the tubes are substantially at ground potential withreference to the radio tubes 6 and I are connected together as bysoldering. ubes 8 and 9 are similarly connected. Plate voltage for theanodes is provided by connecting the midpoint of the effective primaryof the transmission line transformer 46 through a choke coil 5| to thepositive side of a source of voltage 52, with a by-pass condenser 53being used to by pass the radio frequency current to ground. Themid-point of the effective secondary is likewise connected to ground.Due to the use of transmission line transformer 48, the plate circuit isof high plate impedance whereby high frequency energy, there isnegligible inter-electrode coupling between the input and outputcircuits of each tube, the only couplingtherebetween 4 being through theelectronic stream. Since the coupling due to the electronic streams ofthe tubes is balanced by adjusting the potentiometers, it will be seenthat radio frequency balance of each of the modulators is readilyobtained and does not depend upon electrically or capacitively matchingthe tubes.

The anodes of tubes 6 and 'l are connected together by a line 44 whilethe anodes of tubes 8 and 9 are connected together by a line 45, line 44being connected to one end, and line 45 is connected to the other end ofa transmission line type of transformer 46, the output lines 41 and 48of. transformer 46 being connected to the usual type of directionfinding receiver 49. Leads 44 and 45 are arranged to be as short aspossible.

For this purpose the anode tube socket prongs of amplification isobtained, while on the other hand, the output of transformer 46 is oflow 1mpedance which is desirable for a receiver designed to operate on ahigh frequency input of (for example) over 100 megacycles. The output ofthe receiver, which may be a conventional receiver of thesup'er-heterodyne type, including a demodulator or detector, is then fedto a modulator 54. The moduiator'54 is also fed by leads 24-21 withsinusoidal modulating voltages derived from oscillator 22 and phaseshifted in phase shifter 23. These voltages from phase shifter 23 areapplied through the modulator 54 to the deflection plates 55 of acathode ray tube 56. These voltages tend to produce a rotation of thebeam, and a circular trace on the screen 51 of the cathode ray tube.However, these voltages are modulated whenever energy is being receivedon receiver 49 to produce a radial deflection of the trace indicatingthe direction from which signals arrive.

While I have described the specific details of one embodiment of myinvention, it will be apparent that many changes may be made in thesedetails in view of the teachings therein. For example, in place of thecrossed loops l and 2, an Adcock array may be substituted. Furthermoreinstead of using triodes in the electronic goniometer 3, other types oftubes such as for, example, pentodes may be used in place thereof.Accordingly, while I have described above the principles of my inventionin connection with specific apparatus. it is to be clearly understoodthat this description is made only by way of example and not as alimitationon the scope of my invention.

I claim:

A radio direction finder comprising a pair of antennas having differentradiant action directivities; a source of low frequency energy having adual output of which one output is substantially 90 out of phase withthe other; a pair of balanced modulators for modulating radio frequencyenergy derivedfrom one of said antennas with the relatively lowfrequency energy of one phase from said low frequency source, eachmodulator comprising a pair or electron discharge devices each having ananode, cathode, and control electrode. a pair of cathode resistors eachconnected at one end to one of saidcathodes and odes together; adirection finding receiver, a

, transformer having each end of its-primary connected to a separate.pair of anodes in a separate one of said balanced modulators, meanscoupling the secondary of. said transformer to said receiver, a cath odtube, means coupling en- 6 ergy from said low frequency source toproduce a deflection of the beam in said cathode ray tube, UNITED STATESPATENTS and means coupling the output of said receiver to Number NameDate said cathode ray tube to modulate said deflection. 4 L4 Llndenblad1937 JOHN H. NEWI'IT. 5 2,290,958 Ha en July 28, 1942 2,399,586 ToominApr. 30, 1946 REFERENCES CITED 2,403,967 Busignles July 16, 19462,406,800 Busignles Sept. 3, 1946 The following references are of recordin the 2,408,039 Buslgmes Sept. 24' 1946 file of this patent:

